1. Field of the Invention
The present invention relates to a communication connecting device advantageously applicable to a gateway, which connects, e.g., a G3 (Group 3) facsimile apparatus to an IP (Internet Protocol) network, for controlling the transmission rate of packets from a real-time facsimile apparatus or terminal, and a communication rate control method for the same.
2. Description of the Background Art
For facsimile communication using an IP network, a gateway is usually situated between the IP network and an analog facsimile apparatus or communication terminal, e.g., a G3 facsimile apparatus. Serving as an Internet facsimile apparatus, the gateway allows the IP network and G3 facsimile apparatus to surely communicate with each other. A protocol defined by ITU-T (International Telecommunication Union, Telecommunication standardization sector) Recommendation T.30 is assigned to the G3 facsimile apparatus. On the other hand, the Internet facsimile apparatus communicates with a PSTN (Public Switched Telephone Network) in accordance with the above Recommendation T.30 and communicates with the IP network with a protocol defined by ITU-T Recommendation T.38.
Assume that data are sent from one G3 facsimile apparatus (sending apparatus) to another G3 facsimile apparatus (receiving apparatus) via Internet. Then, the sending apparatus first sends a calling tone (CNG) command to the receiving apparatus in accordance with the Recommendation T.30 protocol, requesting the receiving apparatus to return a called station identification (CED) signal. In response, the receiving station sends the CED signal and then sends a digital identification signal (DIS) to the sending apparatus. The DIS signal includes information representative of a communication rate available with the receiving apparatus.
On receiving the DIS signal, the sending apparatus determines a communication rate at which it can communicate with the receiving apparatus. The sending apparatus then sends a digital command signal (DCS) indicative of the determined communication rate to the receiving apparatus. Thereafter, the sending apparatus sends facsimile data to the receiving station.
Assume that the sending apparatus is implemented by a real-time Internet facsimile apparatus. Then, the sending real-time Internet facsimile apparatus also determines a communication rate at which it can communicate with the receiving G3 facsimile apparatus by the above-described procedure. Specifically, the receiving apparatus sends the DIS signal including the communication rate, which is defined by Recommendation T.30, to the sending apparatus. The sending apparatus, however, sends the DSC signal indicative of the communication rate defined by Recommendation T.38 to the receiving apparatus because it is directly connected to the IP network. Specifically, using a traffic capacity of 10 Mbps (megabits per second) or 100 Mbps as a standard, the DCS signal is indicative of a data transmission rate available with 10 BASE, 100 BASE or similar transmission media.
More specifically, a real-time Internet facsimile apparatus is capable of interchanging data even with, e.g., a computer terminal of the type dealing with electronic mails, Internet telephony, video data and so forth. This is why the above-mentioned communication rate is assigned to a real-time Internet facsimile apparatus.
As stated above, the communication rate available with the sending real-time Internet facsimile apparatus is far higher than the communication rate of the receiving G3 facsimile apparatus. Stated another way, the sending apparatus and receiving apparatus cannot negotiate with each other.